Liquid crystal display device

ABSTRACT

Realizes a structure for a transreflective liquid crystal display device in which one pixel is defined by four or more picture elements, the structure providing a high aperture ratio and being suitable for display for which the transmission mode is prioritized. A liquid crystal display device according to the present invention is a transreflective liquid crystal display device, comprising a plurality of picture elements including a first picture element, a second picture element, a third picture element and a fourth picture element for displaying different colors from one another; in which each of the plurality of picture elements includes a transmission area for providing display in a transmission mode and a reflection area for providing display in a reflection mode. Each picture element includes a mesh portion shaped to be meshable with an adjacent picture element; and the reflection area of each picture element is located in the mesh portion.

This application is the U.S. national phase of International ApplicationNo. PCT/JP2007/052962, filed 19 Feb. 2007, which designated the U.S. andclaims priority to Japan Application No. 2006-075083, filed 17 Mar.2006, the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a liquid crystal display deviceproviding color display, and specifically to a transreflective liquidcrystal display device capable of providing display both in atransmission mode and a reflection mode.

BACKGROUND ART

Currently, liquid crystal display devices (hereinafter, also referred tosimply as “LCDs”) are used for various applications. In general LCDs,one pixel is formed of three picture elements respectively for providingdisplay in red, green and blue, which are three primary colors of light,and thus color display can be provided.

However, conventional LCDs have a problem that the range of colors whichcan be displayed (referred to as the “color reproduction range”) isnarrow. FIG. 18 shows a color reproduction range of a conventional LCDwhich provides display using the three primary colors. FIG. 18 is an xychromaticity diagram of an XYZ color representation system, in which atriangle having, as apexes, three points corresponding to the threeprimary colors of red, green and blue represents the color reproductionrange. In the figure, colors of various objects existent in the naturalworld which were found by Pointer are plotted with “x” (see Non-patentDocument No. 1). As understood from FIG. 18, there are colors of objectswhich are not encompassed in the color reproduction range. An LCDproviding display using the three primary colors cannot display a partof the colors of objects.

In order to enlarge the color reproduction range of LCDs, techniques forincreasing the number of primary colors usable for display to four orgreater have been proposed.

For example, as shown in FIG. 19, Patent Document 1 discloses an LCD 800in which one pixel P is formed of six picture elements R, G, B, Ye, Cand M respectively for displaying red, green, blue, yellow, cyan andmagenta. FIG. 20 shows the color reproduction range of the LCD 800. Asshown in FIG. 20, the color reproduction range represented by a hexagonhaving, as apexes, six points corresponding to six primary colorsencompasses substantially all the colors of objects. In this way, thecolor reproduction range can be enlarged by increasing the number ofprimary colors.

Patent Document 1 also discloses an LCD in which one pixel is formed offour picture elements for displaying red, green blue and yellow, and anLCD in which one pixel is formed of five picture elements for displayingred, green blue, yellow and cyan. By using four or more primary colors,an LCD can enlarge the color reproduction range as compared to theconventional LCD providing display using the three primary colors. Inthis specification, LCDs providing display using four or more primarycolors will be collectively referred to as a “multiple primary colorliquid crystal display device (or multiple primary color LCD)”.

On the other hand, LCDs capable of providing high quality display bothoutdoors and indoors have been proposed (for example, Patent Document2). Such LCDs are referred to as “transreflective LCDS” and have areflection area for providing display in a reflection mode and atransmission area for providing display in a transmission mode in onepixel.

FIG. 21 shows an example of a transreflective LCD. An LCD 900 shown inFIG. 21 has a pixel defined by three picture elements R, G and Brespectively for displaying red, green and blue.

The three picture elements R, G and B each have a transmission area Trfor providing display in a transmission mode and a reflection area Rf(hatched in the figure) for providing display in a reflection mode.Typically, the reflection area Rf accommodates a reflective electrodeformed of a conductive material having a high light reflectance such asaluminum or the like. By contrast, the transmission area Tr accommodatesa transmissive electrode formed of a conductive material having a highlight transmittance such as ITO or the like.

The area size ratio of the transmission area Tr and the reflection areaRf is determined based on which mode of display, i.e., the transmissionmode or the reflection mode, is prioritized and to which degree. As thetransmission mode of display is more prioritized, the area size of thetransmission area Tr is set to be larger; whereas as the reflection modeof display is more prioritized, the area size of the reflection area Rfis set to be larger. From the viewpoint of improving the indoor displayquality, the transmission mode of display needs to be prioritized andthe area size of the transmission area is set to be larger.

The reflective electrode and the transmissive electrode are switched toeach other by a thin film transistor 11 provided in each pictureelement. The thin film transistor 11 is supplied with a scanning signalfrom a scanning line 12 and is supplied with a video signal from asignal line 13. A storage capacitance line 14 is provided so as toextend parallel to the scanning line 12. In an area outside the pictureelements, a lattice-shaped (or stripe-shaped) light shielding layer(referred to as “black matrix”) BM is provided.

The lines and the transistors 11 are formed of a light shieldingmaterial and therefore decrease the ratio of an area actuallycontributing to display (referred to as “aperture ratio”) in a liquidcrystal panel. However, in the case where the line extending across thepicture elements (in this example, the scanning line 12) and the thinfilm transistors 11 are located within the reflection area Rf as shownin FIG. 21, the aperture ratio is improved and bright display isrealized.

Patent Document 1: Japanese PCT National-Phase Laid-Open PatentPublication No. 2004-529396

Patent Document 2: Japanese Laid-Open Patent Publication No. 11-101992

Non-patent Document 1: M. R. Pointer, “The gamut of real surfacecolors,” Color Research and Application, Vol. 5, No. 3, pp. 145-155(1980)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, for LCDs in which one pixel is defined by four or more pictureelements such as multiple primary color LCDs, a structure optimum for atransreflective system has not been found. As the number of pictureelements included in one pixel increases, the number of lines and thinfilm transistors also increases and so the aperture ratio decreases.Therefore, when a structure of a transreflective LCD for providingdisplay with three primary colors as shown in FIG. 21 is applied to amultiple primary color LCD as it is, the luminance decreases. Theaperture ratio can be maintained at a relatively high level by locatingthe lines extending across the picture elements or the thin filmtransistors in the reflection area. However, when such a structure isadopted, the area size of the reflection area cannot be made smallerthan a certain level, and accordingly, the area size of the transmissionarea cannot be made much larger. Hence, it is difficult to improve theindoor display quality.

The present invention, made in light of the above-described problems,has an object of, in a transreflective liquid crystal display device inwhich one pixel is defined by four or more picture elements, realizing astructure which provides a high aperture ratio and is suitable fordisplay for which the transmission mode is prioritized.

Means for Solving the Problems

A liquid crystal display device according to the present invention is aliquid crystal display device, comprising a plurality of pictureelements including a first picture element, a second picture element, athird picture element and a fourth picture element for displayingdifferent colors from one another; in which each of the plurality ofpicture elements includes a transmission area for providing display in atransmission mode and a reflection area for providing display in areflection mode. Each of the plurality of picture elements includes amesh portion shaped to be meshable with an adjacent picture element; andthe reflection area of each of the plurality of picture elements islocated in the mesh portion. Thus, the above-described objective isachieved.

In one preferable embodiment, the plurality of picture elements are eachL-shaped.

In one preferable embodiment, the plurality of picture elements define aplurality of pixels each including the first picture element, the secondpicture element, the third picture element and the fourth pictureelement; and the mesh portion of each of the plurality of pictureelements meshes with a picture element belonging to the same pixel.

In one preferable embodiment, the plurality of picture elements define aplurality of pixels each including the first picture element, the secondpicture element, the third picture element and the fourth pictureelement; and the mesh portion of each of the plurality of pictureelements meshes with a picture element belonging to a different pixel.

In one preferable embodiment, the first picture element is a red pictureelement for displaying red, the second picture element is a greenpicture element for displaying green, and the third picture element is ablue picture element for displaying blue.

In one preferable embodiment, the fourth picture element is a whitepicture element for displaying white.

In one preferable embodiment, among the first picture element, thesecond picture element, the third picture element and the fourth pictureelement, two picture elements display colors in a complementaryrelationship to each other; and the mesh portions of the two pictureelements mesh with each other.

In one preferable embodiment, the fourth picture element is a yellowpicture element for displaying yellow.

In one preferable embodiment, the mesh portion of the blue pictureelement and the mesh portion of the yellow picture element mesh witheach other.

In one preferable embodiment, the reflection area of the blue pictureelement has a larger area size than an area size of the reflection areaof the yellow picture element.

In one preferable embodiment, the red picture element, the green pictureelement, the blue picture element and the yellow picture element arearranged in a matrix of 2 rows and 2 columns; and the mesh portion ofthe red picture element, the mesh portion of the green picture element,the mesh portion of the blue picture element and the mesh portion of theyellow picture element are arranged to be continuous like a strip in arow direction.

In one preferable embodiment, the mesh portions arranged to becontinuous like a strip are continues in the order of the mesh portionof the red picture element, the mesh portion of the green pictureelement, the mesh portion of the blue picture element and the meshportion of the yellow picture element; or in the order of the meshportion of the green picture element, the mesh portion of the redpicture element, the mesh portion of the yellow picture element and themesh portion of the blue picture element.

In one preferable embodiment, the mesh portions arranged to becontinuous like a strip are continues in the order of the mesh portionof the red picture element, the mesh portion of the green pictureelement, the mesh portion of the yellow picture element and the meshportion of the blue picture element.

In one preferable embodiment, the liquid crystal display deviceaccording to the present invention includes an active matrix substrateincluding a switching element provided for each of the plurality ofpicture elements; and the switching element is located in the reflectionarea of each of the plurality of picture elements.

Effects of the Invention

According to the present invention, a structure for a transreflectiveliquid crystal display device in which one pixel is defined by four ormore picture element, the structure providing a high aperture ratio andbeing suitable for display for which the transmission mode isprioritized, can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically showing an LCD 100 according to apreferable embodiment of the present invention.

FIGS. 2( a) and (b) are each a plan view schematically showing an LCD700 as a comparative example.

FIG. 3 is a plan view schematically showing the LCD 700 as a comparativeexample.

FIG. 4 is a plan view schematically showing the LCD 100 according to apreferable embodiment of the present invention.

FIG. 5 is an xy chromaticity diagram in which white displayed in areflection mode is plotted in Examples 1 through 5 in which whitebalance in the reflection mode display is adjusted by changing the areasize of the reflection area.

FIG. 6 is a graph illustrating the spectrum characteristic of a colorfilter.

FIG. 7 is a graph illustrating the wavelength dependency of theintensity of light transmitted through a liquid crystal layer.

FIG. 8 is a graph illustrating the spectrum of external light (ambientlight) used for reflection mode display.

FIG. 9( a) shows a structure in which a mesh portion of each pictureelement meshes with a picture element belonging to the same pixel, and(b) shows a structure in which a mesh portion of each picture elementmeshes with a picture element belonging to a different pixel.

FIG. 10( a) schematically shows a white line displayed on a blackbackground by the structure shown in FIG. 9( a), and (b) schematicallyshows a white line displayed on a black background by the structureshown in FIG. 9( b).

FIG. 11 is a plan view showing an exemplary specific structure of theLCD 100 according to a preferable embodiment of the present invention.

FIG. 12 is a cross-sectional view showing the exemplary specificstructure of the LCD 100 according to a preferable embodiment of thepresent invention, taken along line 12A-12A′ of FIG. 11.

FIG. 13 is a plan view showing another exemplary specific structure ofthe LCD 100 according to a preferable embodiment of the presentinvention.

FIGS. 14( a) and (b) are each a plan view showing still anotherexemplary specific structure of the LCD 100 according to a preferableembodiment of the present invention.

FIG. 15( a), (b) and (c) show the relationship between the order ofarrangement of the reflection areas in the picture elements and theluminance of the picture elements.

FIG. 16 is a plan view schematically showing another LCD 200 accordingto a preferable embodiment of the present invention.

FIG. 17 is a cross-sectional view schematically showing the exemplaryspecific structure of the LCD 200 according to a preferable embodimentof the present invention, taken along line 17A-17A′ of FIG. 16.

FIG. 18 shows a color reproduction range of a conventional LCD usingthree primary colors for display.

FIG. 19 schematically shows a conventional multiple color LCD 800.

FIG. 20 shows a color reproduction range of the LCD 800.

FIG. 21 is a plan view schematically showing a conventionaltransreflective LCD 900.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   10 Insulating plate    -   11 Thin film transistor (TFT)    -   12 Scanning line    -   13 Signal line    -   14 Storage capacitance line    -   15 Basecoat film    -   16 Semiconductor layer    -   17 Storage capacitance electrode    -   18 Storage capacitance connection line    -   19 Gate insulating film    -   20 Gate electrode    -   21 First interlayer insulating film    -   22 Source electrode    -   23 Drain electrode    -   24 Second interlayer insulating film    -   25 Picture element electrode    -   25 a Transparent electrode    -   25 b Reflective electrode    -   26 Alignment film    -   27 Conductive member    -   30 Insulating plate    -   31R, 31G, 31B, 31Ye Color filter    -   32 Transparent dielectric layer    -   33 Counter electrode    -   34 Alignment film    -   35 Projection (rivet)    -   40 Liquid crystal layer    -   100 a Active matrix substrate (TFT substrate)    -   100 b Counter substrate    -   100 Liquid crystal display device (LCD)    -   R Red picture element    -   G Green picture element    -   B Blue picture element    -   Ye Yellow picture element    -   Tr Transmission area    -   Rf Reflection area    -   BM Black matrix    -   CH Contact hole

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The present invention is not limited to thefollowing embodiments.

Embodiment 1

FIG. 1 schematically shows a liquid crystal display device (LCD) 100according to this embodiment. The LCD 100 has a plurality of pictureelements including four types of picture elements respectively fordisplaying different colors from each other.

As shown in FIG. 1, the LCD 100 specifically includes a red pictureelement R for displaying red, a green picture element G for displayinggreen, a blue picture element B for displaying blue, and a yellowpicture element Ye for displaying yellow. These four picture elementsdefine one “pixel”. In this embodiment, the red picture element R, thegreen picture element G, the blue picture element B and the yellowpicture element Ye are arranged in a matrix of 2 rows and 2 columns inone pixel. The LCD 100 uses a larger number of primary colors fordisplay than a general LCD which provides display using three primarycolors, and therefore has a larger color reproduction range.

The red picture element R, the green picture element G, the blue pictureelement B and the yellow picture element Ye each have a transmissionarea Tr for providing display in a transmission mode and a reflectionarea Rf (hatched area in the figure) for providing display in areflection mode. In the transmission area Tr, display is provided usinglight from an illumination device (backlight); whereas in the reflectionarea Rf, display is provided using ambient light (external light).

Typically, the reflection area Rf accommodates a reflective electrodefor reflecting light, and the transmission area Tr accommodates atransparent electrode for transmitting light. The reflective electrodeis formed of a conductive material having a high light reflectance suchas aluminum or the like. The reflective electrode is formed of aconductive material having a high light transmittance such as ITO or thelike.

It is preferable that the reflection area Rf and the transmission areaTr are different in the thickness of the liquid crystal layer (cellgap). Specifically, it is preferable that the thickness of the liquidcrystal layer is smaller in the reflection area Rf than in thetransmission area Tr. More specifically, the thickness of the liquidcrystal layer in the reflection area Rf is preferably about ½ of that inthe transmission area Tr. Light incident on the transmission area Trfrom the backlight side passes through the liquid crystal layer onlyonce, whereas light incident on the reflection area Rf from the observerside passes through the liquid crystal layer twice. By making the cellgap of the reflection area Rf smaller than that of the transmission areaTr (such a structure is referred to as a “multi-gap structure”) asdescribed above, the difference in retardation caused by the differencein the number of times that light passes through the liquid crystallayer can be decreased. As a result, the display quality is improved.

In order to realize the multi-gap structure, at least one of a pair ofsubstrates facing each other with the liquid crystal layer locatedbetween has a step. The step can be provided by selectively forming atransparent dielectric layer on a part of the substrate using a resin orthe like.

The LCD 100 further includes thin film transistors (TFT) 11 eachprovided in one picture element, scanning lines 12 for supplying ascanning signal to the TFTs 11, and signal lines 13 for supplying avideo signal to the TFTs 11. The TFT 11 acts as a switching element forswitching the picture element electrode (typically, including thereflective electrode and the transmissive electrode). Herein, for thesake of convenience, the direction in which the scanning lines 12 extendis referred to as a “row direction” and the direction in which thesignal lines 13 extend is referred to as a “column direction”.

The LCD 100 includes storage capacitance lines 14 for forming a storagecapacitance. The storage capacitance lines 14 are formed so as to extendsubstantially parallel to the scanning lines 12. In this embodiment, thestorage capacitance lines 14 are provided outside the picture elements,whereas the scanning lines 12 are provided so as to extend across thepicture elements. The scanning lines 12 extending across the pictureelements and the thin film transistors 11 are located within thereflection area Rf in order to increase the aperture ratio. In an areaoutside the picture elements, a light shielding layer (referred to as“black matrix”) BM is provided so as to surround each picture element.

In a general LCD, as shown in FIG. 21, each picture element isrectangular. By contrast, the picture elements in the LCD 100 in thisembodiment are each L-shaped, and two picture elements adjacent to eachother in the column direction mesh with each other. Namely, each pictureelement has a portion shaped to be meshable with an adjacent pictureelement (referred to as a “mesh portion” in this specification). Thereflection area Rf of each picture element is provided in the meshportion thereof.

In this embodiment, the mesh portion of the red picture element R andthe mesh portion of the green picture element G mesh with each other,and the mesh portion of the blue picture element B and the mesh portionof the yellow picture element Ye mesh with each other. The mesh portionof the red picture element R, the mesh portion of the green pictureelement G, the mesh portion of the blue picture element B and the meshportion of the yellow picture element Ye are arranged continuously likea strip in the row direction. The reflection area Rf of the red pictureelement R, the reflection area Rf of the green picture element G, thereflection area Rf of the blue picture element B and the reflection areaRf of the yellow picture element Ye are also arranged continuously likea strip.

In the LCD 100 as described above, each picture element has a meshportion shaped to be meshable with an adjacent picture element, and thereflection area of each picture element is located in the mesh portion.Owing to such a structure, display for which the transmission mode isprioritized can be realized while the aperture ratio is kept high. Thereason for this will be described, hereinafter.

FIG. 2( a) shows an LCD 700 as a comparative example. The LCD 700 as acomparative example includes a red picture element R, a green pictureelement G, a blue picture element B and a yellow picture element Ye, buteach picture element is rectangular and does not have any mesh portion.

In order to realize display for which the transmission mode isprioritized in the LCD 700, it is necessary to decrease the area size ofthe reflection area Rf and thus to increase the area size of thetransmission area Tr. However, in order to keep the aperture ratio high,the lines, the TFT 11 and the like need to be provided in the reflectionarea Rf. Because there are limitations on the inter-line distances andthe size of the TFTs 11, it is not possible to decrease the area size ofthe reflection area Rf infinitely.

For example, in FIG. 2( b), the width of each reflection area Rf in therow direction (the direction in which the scanning lines 12 extend) isdecreased in order to forcibly decrease the area size of the reflectionarea Rf. In this case, only a part of the scanning line 12 extendingacross the picture element (represented with hatching in the figure) canbe located in the reflection area Rf, and accordingly, the apertureratio is decreased.

By contrast, in the LCD 100 shown in FIG. 1, each picture elementincludes a mesh portion shaped to be meshable with an adjacent pictureelement, and the reflection area Rf is located in the mesh portion. Inthis case, the area size of the reflection area Rf can be sufficientlydecreased while accommodating the lines extending across the pictureelement and TFT 11. Accordingly, the area size of the transmission areaTr can be sufficiently increased, and thus the indoor display qualitycan be sufficiently improved.

With the structure shown in FIG. 2( b), the reflection areas Rf arelocated like islands. Therefore, when providing transparent dielectriclayers for forming a multiple gap structure, alignment margins need tobe taken into consideration both in the row direction and the columndirection. By contrast, with the LCD 100 in this embodiment, thereflection area Rf is located in each mesh portion, and as a result, thereflection areas Rf are located continuously like a strip. Accordingly,the dielectric layers may also be formed continuously like a strip.Alignment margins do not need to be taken into consideration in thedirection in which the dielectric layers are continuous. Therefore, theaperture ratio of the reflection areas Rf (reflection aperture ratio)can be improved.

In addition, the LCD 100 in this embodiment is also superior on thecapability of realizing preferable white balance both in thetransmission mode and the reflection mode. The reason for this will bedescribed, hereinafter.

For providing display with four primary colors of red, green, blue andadditionally yellow, white balance is likely to be destroyed. As aresult, the displayed white color is yellowish (i.e., the colortemperature of white is lowered). In transmission mode display,preferable white balance can be realized by adjusting the light sourceof backlight (specifically, by using a light source for emittingslightly bluish white light). In the reflection mode, however, ambientlight is used for display and therefore, white balance cannot beadjusted in such a manner.

Thus, it is conceivable to adjust the white balance in the reflectionmode by adjusting the area sizes of the reflection areas Rf.Specifically, by making the area size of the reflection area Rf of theblue picture element B larger than the area size of the reflection areaRf of the yellow picture element Ye, the white color in the reflectionmode can be prevented from becoming yellowish.

However, adjusting the white balance in such a manner presents anotherproblem. For example, it is assumed that from the LCD 700 shown in FIG.2( b) as a comparative example, the area size of the reflection area Rfof the blue picture element B is increased and the area size of thereflection area Rf of the yellow picture element Ye is decreased. Then,as shown in FIG. 3, the area size of the transmission area Tr of theblue picture element B is made smaller than the area size of thetransmission area Tr of the yellow blue picture element Ye. As a result,the white color in the transmission mode becomes yellowish. In order toprevent this, it is conceivable to replace the light source of theillumination device with a light source which emits further bluishlight. However, when the light from the light source becomes morebluish, the luminance of the backlight is decreased.

By contrast, with the LCD 100 in this embodiment, the mesh portions oftwo picture elements for displaying colors in a complementaryrelationship to each other, i.e., the mesh portion of the blue pictureelement B and the mesh portion of the yellow picture element Ye meshwith each other. Therefore, by adjusting the area sizes of these meshportions, as shown in FIG. 4, the area size ratio of the reflection areaRf of the blue picture element B and the reflection area Rf of theyellow picture element Ye can be changed without changing the area sizeratio of the transmission area Tr of the blue picture element B and thetransmission area Tr of the yellow picture element Ye (specifically, thearea size of the reflection area Rf of the blue picture element B can bemade larger than the area size of the reflection area Rf of the yellowpicture element Ye). Therefore, the white balance in the reflection modedisplay can be adjusted without destroying the white balance in thetransmission mode display. As a result, preferable white balance can berealized both in the transmission mode and the reflection mode.

Table 1 and FIG. 5 show examples (Examples 1 through 5) in which thewhite balance in the reflection mode display is adjusted by changing thearea sizes of the reflection areas Rf. Table 1 shows the relationship ofthe area sizes of the reflection areas Rf of the red picture element R,the green picture element G, the blue picture element B and the yellowpicture element Ye, with the color temperature and the xy chromaticityof white displayed in the reflection mode. FIG. 5 is an xy chromaticitydiagram in which white displayed in the reflection mode in Examples 1through 5 is plotted. Data shown herein is of an LCD which uses thefollowing for the reflection mode display: a color filter having thespectrum characteristic shown in FIG. 6, a liquid crystal layerexhibiting the wavelength dependency of the transmitted light intensityshown in FIG. 7, and external light (ambient light) having the spectrumshown in FIG. 8.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Red 1.0 1.0 1.0 1.0 0.8 Green 1.01.0 1.0 1.0 1.2 Blue 1.0 1.2 1.3 1.4 1.3 Yellow 1.0 0.8 0.7 0.6 0.7Color 3925 5041 6150 8101 7234 temperature x 0.3905 0.3439 0.3197 0.29620.2947 y 0.4038 0.3523 0.3247 0.2975 0.3525

As shown in Table 1 and FIG. 5, in Example 1, the area sizes of thereflection areas Rf of the red picture element R, the green pictureelement G, the blue picture element B and the yellow picture element Yeare equal to one another. Therefore, the color temperature of white islow and white is slightly yellowish. By contrast, in Examples 2, 3 and4, the area size of the reflection area Rf of the blue picture element Bis larger than the area size of the reflection area Rf of the yellowpicture element Ye. Therefore, the color temperature of white can bemade higher. As understood from comparing Examples 2, 3 and 4, as thearea size of the reflection area Rf of the blue picture element B ismade larger with respect to the area size of the reflection area Rf ofthe yellow picture element Ye, the color temperature of white is raised.As understood from comparing Examples 3 and 5, the color temperature ofwhite can be further raised by decreasing the area size of thereflection area Rf of the red picture element R in addition to makingthe area size of the reflection area Rf of the blue picture element Blarger than the area size of the reflection area Rf of the yellowpicture element Ye.

In this embodiment, as shown in FIG. 9( a), the mesh portion of eachpicture element meshes with a picture element belonging to the samepixel. The present invention is not limited to this. As shown in FIG. 9(b), the mesh portion of each picture element may mesh with a pictureelement belonging to a different pixel.

In the structure shown in FIG. 9( b), each picture element is L-shapedand includes a mesh portion. The mesh portion of each picture elementmeshes with a picture element belonging to a different pixel, not with apicture element belonging to the same pixel. Specifically, the meshportion of the red picture element R of a certain pixel meshes with thegreen picture element G belonging to a pixel below the certain pixel,and the mesh portion of the green picture element G of the certain pixelmeshes with the red picture element R belonging to a pixel above thecertain pixel. The mesh portion of the blue picture element B of thecertain pixel meshes with the yellow picture element Ye belonging to apixel below the certain pixel, and the mesh portion of the yellowpicture element Ye of the certain pixel meshes with the blue pictureelement B belonging to a pixel above the certain pixel. With such astructure also, the above-described effect can be provided.

In the case where the picture elements are located such that the meshportion of each picture element meshes with a picture element belongingto a different pixel, a white line on a black background can bedisplayed in a preferable manner regardless of the direction in whichthe line extends.

In FIG. 9( a), the picture elements are located such that the meshportion of each picture element meshes with a picture element belongingto the same pixel. In this case, the reflection areas Rf are arranged soas to be continuous like a strip in the row direction. Therefore, asshown in FIG. 10( a), a white line on a black background extending inthe row direction and a white line on the black background extending inthe column direction are displayed as having significantly differentthicknesses.

By contrast, in FIG. 9( b), the picture elements are located such thatthe mesh portion of each picture element meshes with a picture elementbelonging to a different pixel. In this case, in one pixel, thereflection areas Rf are located at substantially the same distance fromthe center of the pixel. Therefore, as shown in FIG. 10( b), a whiteline on a black background extending in the row direction and a whiteline on the black background extending in the column direction aredisplayed as having substantially the same thickness. Thus, preferabledisplay can be realized regardless of the direction in which the lineextends.

Next, a more specific structure of the LCD 100 in this embodiment willbe described. FIG. 11 is a plan view showing an exemplary specificstructure of the LCD 100, and FIG. 12 is a cross-sectional view takenalong line 12A-12A′ of FIG. 11. In FIG. 11, the reflection area Rf ofeach picture element is shown without hatching for a clearer appearance.

The LCD 100 includes an active matrix substrate (hereinafter, referredto as a “TFT substrate”) 100 a including a TFT 11 provided for each of aplurality of picture elements, a color filter 100 b facing the TFTsubstrate 100 a, and a liquid crystal layer 40 provided between thesesubstrates.

The TFT substrate 100 a has a structure in which many films are stackedon a transparent insulating plate (e.g., a glass plate) 10. Hereinafter,the structure of the TFT substrate 100 a will be described morespecifically.

First, a basecoat film 15 is formed so as to cover substantially theentirety of the insulating plate 10. Semiconductor layers 16 forming theTFTs 11, storage capacitance electrodes 17 each forming a storagecapacitance, and storage capacitance connection lines 18 forelectrically connecting the semiconductor layers 16 and the storagecapacitance electrodes 17 are provided on the basecoat film 15. Thesemiconductor layers 16, the storage capacitance electrodes 17 and thestorage capacitance connection lines 18 are formed of one, samesemiconductor film.

A gate insulating film 19 is formed so as to cover the semiconductorlayers 16, the storage capacitance electrodes 17 and the storagecapacitance connection lines 18. The scanning lines 12, storagecapacitance lines 14 and gate electrodes 20 extending from the scanninglines 12 are provided on the gate insulating film 19. The storagecapacitance lines 14 face the storage capacitance electrodes 17 with thegate insulating film 19 provided therebetween. Each storage capacitanceline 14, the corresponding storage capacitance electrode 17 and the gateinsulating film 19 located therebetween form a storage capacitance Cs.In FIG. 11, the storage capacitances for the red picture element R, thegreen picture element G, the blue picture element B and the yellowpicture element Ye are respectively represented as Cs(R), Cs(G), Cs(B)and Cs(Ye).

A first interlayer insulating film (e.g., an inorganic insulating film)21 is formed so as to cover the scanning lines 12 and the like. Thesignal lines 13, source electrodes 22 and drain electrodes 23 are formedon the first interlayer insulating film 21. Each source electrode 22 andthe corresponding drain electrode 23 are connected to the correspondingsemiconductor layer 16 via a contact hole CH formed in the gateinsulating film 19 and the first interlayer insulating film 21.

A second interlayer insulating film (e.g., a transparent resin film) 24is formed so as to cover the signal lines 13 and the like. Pictureelement electrodes 25 each including a transparent electrode 25 a and areflective electrode 25 b are formed on the second interlayer insulatingfilm 24. Each picture element electrode 25 is connected to thecorresponding drain electrode 23 via a contact hole CH formed in thesecond interlayer insulating film 24. An alignment film 26 is formed soas to cover the picture element electrodes 25.

The color filter substrate 100 b includes a transparent insulating plate(e.g., a glass plate) 30, and a red color filter 31R, a green colorfilter 31G, a blue color filter 31B, a yellow color filter 31Ye and ablack matrix BM formed on the transparent insulating plate 30. On thesecolor filters and the black matrix BM, a transparent dielectric layer(e.g., a transparent resin layer) 32 is selectively formed only in thereflection areas Rf. A counter electrode 33 and an alignment film 34 areprovided so as to cover the transparent dielectric layer 32.

As the liquid crystal layer 40, various display modes of liquid crystallayer can be used. The transparent dielectric layer 32 selectivelyformed in the reflection area Rf forms a step in the color filter 10 b.Because of this, the thickness of the liquid crystal layer 40 in thereflection area Rf and the thickness of the liquid crystal layer 40 inthe transmission area Tr are different.

The LCD 100 having the structure shown in FIGS. 11 and 12 may beproduced by any of various known production methods.

FIG. 11 shows four picture elements and two scanning lines. The TFTs 11for the two picture elements shown above (specifically, the greenpicture element G and the yellow picture element Ye) are connected tothe lower scanning line 12, whereas the TFTs 11 for the two pictureelements shown below (specifically, the red picture element R and theblue picture element B) are connected to the upper scanning line 12.

By contrast, as shown in FIG. 13, the TFTs 11 for the green pictureelement G and the yellow picture element Ye shown above may be connectedto the upper scanning line 12, and the TFTs 11 for the red pictureelement R and the blue picture element B shown below may be connected tothe lower scanning line 12.

With either structure, it is preferable that the storage capacitanceconnection line 18 for each picture element is located so as to extendbelow, not the scanning line 12 for driving this picture element, thescanning line 12 for driving the adjacent picture element, as shown inFIGS. 11 and 13. For example, regarding the red picture element R inFIG. 11, the storage capacitance connection line 18 for this red pictureelement R is located so as to extend below the scanning line 12 fordriving the green picture element G (lower scanning line in the figure),not the scanning line 12 for driving the red picture element R (upperscanning line in the figure).

At a portion where the storage capacitance connection line 18 and thescanning line 12 cross each other, a parasitic capacitance is formed.Where the storage capacitance connection line 18 of each picture elementextends below the scanning line 12 for driving this picture element, theparasitic capacitance causes a pull-in potential in a gate-off state,which influences the optimum counter electrode potential. For thisreason, it is preferable that the storage capacitance connection line 18of each picture element is located so as to extend below the scanningline 12 for driving the adjacent picture element.

With the structure shown in FIG. 13, in order to locate the storagecapacitance connection line 18 of each picture element so as to extendbelow the scanning line 12 for driving an adjacent picture element, thestorage capacitance is formed in the adjacent picture element.Specifically, the storage capacitance Cs(R) for the red picture elementR is formed in the green picture element G, and the storage capacitanceCs(B) for the blue picture element B is formed in the yellow pictureelement Ye. The storage capacitance Cs(G) for the green picture elementG is formed in the red picture element R, and the storage capacitanceCs(Ye) for the yellow picture element Ye is formed in the blue pictureelement B.

As shown in FIG. 13, where the storage capacitance connection line 18extends across another picture element, a capacitance is formed betweenthe picture elements. Therefore, after a signal is written in a pictureelement, pull-in occurs by the influence of the potential change in theadjacent picture element, and the voltage transmittance characteristicis shifted. As a result, a difference in the voltage transmittancecharacteristic is made between the two picture elements shown above (thegreen picture element G and the yellow picture element Ye) and the twopicture elements shown below (the red picture element R and the bluepicture element B).

Such a problem can be alleviated by setting γ for each of the redpicture element R, the green picture element G, the blue picture elementB and the yellow picture element Ye independently.

Even with the structure shown in FIG. 11, the inter-picture elementcapacitance may be dispersed among the picture elements to cause adifference in the voltage transmittance characteristic. In such a casealso, γ may be set for each of the red picture element R, the greenpicture element G, the blue picture element B and the yellow pictureelement Ye independently.

In the above examples, as shown in FIG. 1 and the like, the meshportions arranged like a strip are continuous in the order of the meshportion of the red picture element R, the mesh portion of the greenpicture element G, the mesh portion of the blue picture element B andthe mesh portion of the yellow picture element Ye. Thus, the reflectionareas Rf are continuous in the order of red, green, blue and yellow ineach picture element. The order of the mesh portions and the reflectionareas Rf is not limited to this.

For example, as shown in FIGS. 14( a) and (b), the mesh portions may becontinuous in the order of the mesh portion of the red picture elementR, the mesh portion of the green picture element G, the mesh portion ofthe yellow picture element Ye and the mesh portion of the blue pictureelement B, and thus the reflection areas Rf of the picture elements maybe continuous in the order of red, green, yellow and blue in eachpicture element.

In general, among the red picture element R, the green picture elementG, the blue picture element B and the yellow picture element Ye, the redpicture element R and the blue picture element B have a relatively lowluminance, whereas the green picture element G and the yellow pictureelement Ye have a relatively high luminance. Therefore, where thereflection areas Rf are continuous in the order of red, green, blue andyellow in a picture element, the reflection areas Rf having a lowluminance and the reflection areas Rf having a high luminance arealternately located as schematically shown in FIG. 15( a). Hence, asingle-color image can be displayed uniformly.

By contrast, where the reflection areas Rf are continuous in the orderof red, green, yellow and blue in a picture element, the reflectionareas Rf having a high luminance are located at the center of the pixelas schematically shown in FIG. 15( b). Hence, when a white line on ablack background or a black line on a white background is displayed, theline can be prevented from being edged with a different color.

The mesh portions may be arranged in the order of the mesh portion ofthe green picture element G, the mesh portion of the red picture elementR, the mesh portion of the yellow picture element Ye and the meshportion of the blue picture element B. With such an order, thereflection areas Rf are continuous in the order of green, red, yellowand blue in a picture element. Therefore, the reflection areas Rf havinga low luminance and the reflection areas Rf having a high luminance arealternately located as schematically shown in FIG. 15( c). In this casealso, the effect of displaying a single-color image uniformly can beprovided.

Embodiment 2

With reference to FIGS. 16 and 17, an LCD 200 according to thisembodiment will be described. FIG. 16 is a plan view schematicallyshowing the LCD 200, and FIG. 17 is a cross-sectional view taken alongline 17A-17A′ of FIG. 16. Hereinafter, the LCD 200 will be describedmainly regarding differences from the LCD 100 in Embodiment 1.

The LCD 200 according to this embodiment provides display in a CPA(Continuous Pinwheel Alignment) mode. In the CPA mode, an opening or acut-out portion is provided in one of the electrodes facing each otherwith a vertical alignment type liquid crystal layer locatedtherebetween. An oblique electric field generated at edges of theopening or the cut-out portion is used to radially orient liquid crystalmolecules. Owing to this, high quality display with a wide viewing angleis realized. The CPA mode is disclosed in, for example, JapaneseLaid-Open Patent Publications Nos. 2003-43525 and 2002-202511.

The picture element electrodes 25 provided in a TFT substrate 200 a ofthe LCD 200 each have an opening and/or cut-out portion (neither isshown). When a voltage is applied between the picture element electrode25 and a counter electrode 33, an oblique electric field is generated atedges of the opening or cut-out portion. The oblique electric fieldcontrols the direction in which liquid crystal molecules in the liquidcrystal layer 40 are tilted when a voltage is applied. Therefore, in theliquid crystal layer 40, a plurality of areas in which the liquidcrystal molecules are radially oriented are formed. Each of the areasthus formed is referred to as a “liquid crystal domain”.

In this embodiment, projections (rivets) 35 for stabilizing theorientation of the liquid crystal domains are formed in the countersubstrate 200 b. The projections 35 are each provided at a positionsubstantially corresponding to the center of the liquid crystal domainformed when a voltage is applied. The projections 35 are formed of, forexample, a transparent resin.

In the LCD 100 shown in FIG. 11, the storage capacitance connection line18 extending from the storage capacitance electrode 17 is directlyconnected to the semiconductor layer 16, and the storage capacitanceconnection line 18 extends across the picture element from the storagecapacitance electrode 17 to the semiconductor layer 16.

By contrast, in this embodiment, the storage capacitance connection line18 is connected to the semiconductor layer 16 via a conductive member27, formed of the same conductive film as the source electrode 22 andthe drain electrode 23, and the picture element electrode 25 and thedrain electrode 23. The storage capacitance connection line 18 is formedon the conductive member 27 in a contact hole CH formed at a positionoverlapping the projection 35, and the conductive member 27 is connectedto the picture element electrode 25 in a contact hole CH formed at aposition overlapping the projection 35.

The storage capacitance connection line 18 is formed of a semiconductorfilm and so has a low light transmittance (e.g., about 50%). In thisembodiment, the storage capacitance connection line 18 only needs toextend to a position overlapping the projection 35. Therefore, thereduction in the light transmittance caused by the storage capacitanceconnection line 18 can be suppressed, and brighter display can berealized. The liquid crystal layer in an area overlapping the projection35 does not much contribute to display (having a low lighttransmittance) anyways. Therefore, the reduction in the transmittancecaused by a contact hole formed in this area does not present anyproblem.

In Embodiments 1 and 2 described above, the present invention has beendescribed with multiple primary color LCDs in which display is providedusing four or more primary colors. The present invention is not limitedto multiple primary color LCDs, and is widely usable for transreflectiveLCDs in which one pixel is defined by four or more picture elements.

For example, the present invention is usable for an LCD in which onepixel is defined by four picture elements, i.e., a red picture elementfor displaying red, a green picture element for displaying green, a bluepicture element for displaying blue and a white picture element fordisplaying white. Where the three picture elements for displaying thethree primary colors are combined with a white picture element fordisplaying white, the luminance of each pixel is increased and stillbrighter display can be realized.

INDUSTRIAL APPLICABILITY

According to the present invention, a structure for a transreflectiveliquid crystal display device in which one pixel is defined by four ormore picture elements, the structure providing provides a high apertureratio and being is suitable for display for which the transmission modeis prioritized, can be realized.

The present invention is preferably usable for a transreflective liquidcrystal display device in which one pixel is defined by four or morepicture elements and also for a multiple primary color liquid crystaldisplay device providing display using four or more primary colors.

1. A liquid crystal display device, comprising: a plurality of pictureelements including a first picture element, a second picture element, athird picture element and a fourth picture element for displayingdifferent colors from one another; wherein: each of the plurality ofpicture elements includes a transmission area for providing display in atransmission mode and a reflection area for providing display in areflection mode; each of the plurality of picture elements includes amesh portion shaped to be meshable with an adjacent picture element; andthe reflection area of each of the plurality of picture elements islocated in the mesh portion.
 2. The liquid crystal display device ofclaim 1, wherein the plurality of picture elements are each L-shaped. 3.The liquid crystal display device of claim 1, wherein: the plurality ofpicture elements define a plurality of pixels each including the firstpicture element, the second picture element, the third picture elementand the fourth picture element; and the mesh portion of each of theplurality of picture elements meshes with a picture element belonging tothe same pixel.
 4. The liquid crystal display device of claim 1,wherein: the plurality of picture elements define a plurality of pixelseach including the first picture element, the second picture element,the third picture element and the fourth picture element; and the meshportion of each of the plurality of picture elements meshes with apicture element belonging to a different pixel.
 5. The liquid crystaldisplay device of claim 1, wherein the first picture element is a redpicture element for displaying red, the second picture element is agreen picture element for displaying green, and the third pictureelement is a blue picture element for displaying blue.
 6. The liquidcrystal display device of claim 5, wherein the fourth picture element isa white picture element for displaying white.
 7. The liquid crystaldisplay device of claim 1, wherein: among the first picture element, thesecond picture element, the third picture element and the fourth pictureelement, two picture elements display colors in a complementaryrelationship to each other; and the mesh portions of the two pictureelements mesh with each other.
 8. The liquid crystal display device ofclaim 5, wherein the fourth picture element is a yellow picture elementfor displaying yellow.
 9. The liquid crystal display device of claim 8,wherein the mesh portion of the blue picture element and the meshportion of the yellow picture element mesh with each other.
 10. Theliquid crystal display device of claim 9, wherein the reflection area ofthe blue picture element has a larger area size than an area size of thereflection area of the yellow picture element.
 11. The liquid crystaldisplay device of claim 8, wherein the red picture element, the greenpicture element, the blue picture element and the yellow picture elementare arranged in a matrix of 2 rows and 2 columns; and the mesh portionof the red picture element, the mesh portion of the green pictureelement, the mesh portion of the blue picture element and the meshportion of the yellow picture element are arranged to be continuous likea strip in a row direction.
 12. The liquid crystal display device ofclaim 11, wherein the mesh portions arranged to be continuous like astrip are continues in the order of the mesh portion of the red pictureelement, the mesh portion of the green picture element, the mesh portionof the blue picture element and the mesh portion of the yellow pictureelement; or in the order of the mesh portion of the green pictureelement, the mesh portion of the red picture element, the mesh portionof the yellow picture element and the mesh portion of the blue pictureelement.
 13. The liquid crystal display device of claim 11, wherein themesh portions arranged to be continuous like a strip are continues inthe order of the mesh portion of the red picture element, the meshportion of the green picture element, the mesh portion of the yellowpicture element and the mesh portion of the blue picture element. 14.The liquid crystal display device of claim 1, wherein: the liquidcrystal display device includes an active matrix substrate including aswitching element provided for each of the plurality of pictureelements; and the switching element is located in the reflection area ofeach of the plurality of picture elements.